Underwire brassiere are available in a wide variety of configurations with underwires which can be made of metal, of plastic or plastic-coated metal, which are round or flattened or of hybrid configuration, which may have rounded ends to facilitate insertion into a stitched channel along the bottom of a brassiere cup to lie against the sternum of the wearer, may have stitching flanges enabling them at various locations to be stitched into the garment and may have configurations which change along the length so as to have variable flexibility within the plane of the underwire or transverse to that plane.
The underwire imparts shape to the cup of the brassiere and has a stiffness or flexibility required to maintain a particular shape or allow various degrees of mobility. The underwire may, in addition, be received under a certain prestress in the channel beneath and around the cup so as to press inward against the breast for enhancement purposes.
Underwires of various shapes are also available in various sizes to accommodate different bust sizes and breast shapes and sizes.